1. Field of the Invention
The present invention relates to a compact, conventional propeller propulsion system for a floating structure, and more specifically the present invention relates to the arrangement and use of a gear arrangement comprising an angular gear in an addition to the hull of the floating structure.
2. Description of Related Art
A floating structure may comprise different types of vessels, semi-submersible platforms, barges etc., the pontoons of the semi-submersible platform then being capable of being regarded as forming a hull of the floating structure.
In connection with the offshore production of oil and gas there are a number of vessels that are adapted to carry out a very few specialised operations. Steadily increasing and more demanding activities offshore have however led to the development of a number of different types of so-called OVS vessels (Offshore Support Vessels), which are vessels that are able to carry out a far higher number of operations and/or services than conventional specialised vessels. This has resulted in such multipurpose vessels having a greater number of persons on board the vessel, in view of the fact that one or more persons will be responsible for their own work tasks. As a consequence of this, these vessels will in the future be subject to a new and more stringent legislative regime, which will include more rigorous requirements concerning the division of the vessel into watertight sections.
The forthcoming rule changes will be difficult to comply with in the case of some types of OVS vessels, for example, anchor handling vessels, as these vessels are built with long propeller shafts extending through large parts of the vessel (diesel-mechanical solutions). These types of solutions take up a great deal of space, thereby substantially reducing the vessel's load capacity. In view of this, a number of vessels have been built with diesel-electrical solutions, which has resulted in a reduction in the length of the propeller shafts. Such solutions will also be more attractive when the propulsion system is used on low-load and part-load rather than pure diesel-mechanical solutions.
Another type of solution which has eliminated the long propeller shafts is so-called azimuth thrusters, which thrusters are used for both propulsion and manoeuvring of the vessel. An azimuth thruster is a separate unit that is mounted in a receiving space in the vessel, and which can be turned 360° about its own axis. Such solutions will however mean that the vessel will have to dock during maintenance, replacement or repairs of the azimuth thruster. Angle drives and gearwheels in such an azimuth thruster will moreover be far more subject to wear and damage, as the pushing and pulling force of the propeller will result in the angle drives and gearwheels being displaced relative to each other, which will mean that they are subjected to greater loads.